4 * Copyright (c) 2018, Arm Limited.
5 * SPDX-License-Identifier: MIT
10 #define N (1 << LOG2_TABLE_BITS)
12 const struct log2_data __log2_data
= {
13 // First coefficient: 0x1.71547652b82fe1777d0ffda0d24p0
14 .invln2hi
= 0x1.7154765200000p
+0,
15 .invln2lo
= 0x1.705fc2eefa200p
-33,
17 // relative error: 0x1.2fad8188p-63
18 // in -0x1.5b51p-5 0x1.6ab2p-5
19 -0x1.71547652b82fep
-1,
21 -0x1.71547652b7c3fp
-2,
23 -0x1.ec709dd768fe5p
-3,
25 -0x1.7153fbc64a79bp
-3,
27 -0x1.289e4a72c383cp
-3,
31 // relative error: 0x1.a72c2bf8p-58
32 // abs error: 0x1.67a552c8p-66
33 // in -0x1.f45p-8 0x1.f45p-8
34 -0x1.71547652b8339p
-1,
36 -0x1.7154764702ffbp
-2,
38 -0x1.ec7b328ea92bcp
-3,
44 log2(x) = k + log2(c) + log2(z/c)
45 log2(z/c) = poly(z/c - 1)
47 where z is in [1.6p-1; 1.6p0] which is split into N subintervals and z falls
48 into the ith one, then table entries are computed as
51 tab[i].logc = (double)log2(c)
52 tab2[i].chi = (double)c
53 tab2[i].clo = (double)(c - (double)c)
55 where c is near the center of the subinterval and is chosen by trying +-2^29
56 floating point invc candidates around 1/center and selecting one for which
58 1) the rounding error in 0x1.8p10 + logc is 0,
59 2) the rounding error in z - chi - clo is < 0x1p-64 and
60 3) the rounding error in (double)log2(c) is minimized (< 0x1p-68).
62 Note: 1) ensures that k + logc can be computed without rounding error, 2)
63 ensures that z/c - 1 can be computed as (z - chi - clo)*invc with close to a
64 single rounding error when there is no fast fma for z*invc - 1, 3) ensures
65 that logc + poly(z/c - 1) has small error, however near x == 1 when
66 |log2(x)| < 0x1p-4, this is not enough so that is special cased. */
68 {0x1.724286bb1acf8p
+0, -0x1.1095feecdb000p
-1},
69 {0x1.6e1f766d2cca1p
+0, -0x1.08494bd76d000p
-1},
70 {0x1.6a13d0e30d48ap
+0, -0x1.00143aee8f800p
-1},
71 {0x1.661ec32d06c85p
+0, -0x1.efec5360b4000p
-2},
72 {0x1.623fa951198f8p
+0, -0x1.dfdd91ab7e000p
-2},
73 {0x1.5e75ba4cf026cp
+0, -0x1.cffae0cc79000p
-2},
74 {0x1.5ac055a214fb8p
+0, -0x1.c043811fda000p
-2},
75 {0x1.571ed0f166e1ep
+0, -0x1.b0b67323ae000p
-2},
76 {0x1.53909590bf835p
+0, -0x1.a152f5a2db000p
-2},
77 {0x1.5014fed61adddp
+0, -0x1.9217f5af86000p
-2},
78 {0x1.4cab88e487bd0p
+0, -0x1.8304db0719000p
-2},
79 {0x1.49539b4334feep
+0, -0x1.74189f9a9e000p
-2},
80 {0x1.460cbdfafd569p
+0, -0x1.6552bb5199000p
-2},
81 {0x1.42d664ee4b953p
+0, -0x1.56b23a29b1000p
-2},
82 {0x1.3fb01111dd8a6p
+0, -0x1.483650f5fa000p
-2},
83 {0x1.3c995b70c5836p
+0, -0x1.39de937f6a000p
-2},
84 {0x1.3991c4ab6fd4ap
+0, -0x1.2baa1538d6000p
-2},
85 {0x1.3698e0ce099b5p
+0, -0x1.1d98340ca4000p
-2},
86 {0x1.33ae48213e7b2p
+0, -0x1.0fa853a40e000p
-2},
87 {0x1.30d191985bdb1p
+0, -0x1.01d9c32e73000p
-2},
88 {0x1.2e025cab271d7p
+0, -0x1.e857da2fa6000p
-3},
89 {0x1.2b404cf13cd82p
+0, -0x1.cd3c8633d8000p
-3},
90 {0x1.288b02c7ccb50p
+0, -0x1.b26034c14a000p
-3},
91 {0x1.25e2263944de5p
+0, -0x1.97c1c2f4fe000p
-3},
92 {0x1.234563d8615b1p
+0, -0x1.7d6023f800000p
-3},
93 {0x1.20b46e33eaf38p
+0, -0x1.633a71a05e000p
-3},
94 {0x1.1e2eefdcda3ddp
+0, -0x1.494f5e9570000p
-3},
95 {0x1.1bb4a580b3930p
+0, -0x1.2f9e424e0a000p
-3},
96 {0x1.19453847f2200p
+0, -0x1.162595afdc000p
-3},
97 {0x1.16e06c0d5d73cp
+0, -0x1.f9c9a75bd8000p
-4},
98 {0x1.1485f47b7e4c2p
+0, -0x1.c7b575bf9c000p
-4},
99 {0x1.12358ad0085d1p
+0, -0x1.960c60ff48000p
-4},
100 {0x1.0fef00f532227p
+0, -0x1.64ce247b60000p
-4},
101 {0x1.0db2077d03a8fp
+0, -0x1.33f78b2014000p
-4},
102 {0x1.0b7e6d65980d9p
+0, -0x1.0387d1a42c000p
-4},
103 {0x1.0953efe7b408dp
+0, -0x1.a6f9208b50000p
-5},
104 {0x1.07325cac53b83p
+0, -0x1.47a954f770000p
-5},
105 {0x1.05197e40d1b5cp
+0, -0x1.d23a8c50c0000p
-6},
106 {0x1.03091c1208ea2p
+0, -0x1.16a2629780000p
-6},
107 {0x1.0101025b37e21p
+0, -0x1.720f8d8e80000p
-8},
108 {0x1.fc07ef9caa76bp
-1, 0x1.6fe53b1500000p
-7},
109 {0x1.f4465d3f6f184p
-1, 0x1.11ccce10f8000p
-5},
110 {0x1.ecc079f84107fp
-1, 0x1.c4dfc8c8b8000p
-5},
111 {0x1.e573a99975ae8p
-1, 0x1.3aa321e574000p
-4},
112 {0x1.de5d6f0bd3de6p
-1, 0x1.918a0d08b8000p
-4},
113 {0x1.d77b681ff38b3p
-1, 0x1.e72e9da044000p
-4},
114 {0x1.d0cb5724de943p
-1, 0x1.1dcd2507f6000p
-3},
115 {0x1.ca4b2dc0e7563p
-1, 0x1.476ab03dea000p
-3},
116 {0x1.c3f8ee8d6cb51p
-1, 0x1.7074377e22000p
-3},
117 {0x1.bdd2b4f020c4cp
-1, 0x1.98ede8ba94000p
-3},
118 {0x1.b7d6c006015cap
-1, 0x1.c0db86ad2e000p
-3},
119 {0x1.b20366e2e338fp
-1, 0x1.e840aafcee000p
-3},
120 {0x1.ac57026295039p
-1, 0x1.0790ab4678000p
-2},
121 {0x1.a6d01bc2731ddp
-1, 0x1.1ac056801c000p
-2},
122 {0x1.a16d3bc3ff18bp
-1, 0x1.2db11d4fee000p
-2},
123 {0x1.9c2d14967feadp
-1, 0x1.406464ec58000p
-2},
124 {0x1.970e4f47c9902p
-1, 0x1.52dbe093af000p
-2},
125 {0x1.920fb3982bcf2p
-1, 0x1.651902050d000p
-2},
126 {0x1.8d30187f759f1p
-1, 0x1.771d2cdeaf000p
-2},
127 {0x1.886e5ebb9f66dp
-1, 0x1.88e9c857d9000p
-2},
128 {0x1.83c97b658b994p
-1, 0x1.9a80155e16000p
-2},
129 {0x1.7f405ffc61022p
-1, 0x1.abe186ed3d000p
-2},
130 {0x1.7ad22181415cap
-1, 0x1.bd0f2aea0e000p
-2},
131 {0x1.767dcf99eff8cp
-1, 0x1.ce0a43dbf4000p
-2},
135 {0x1.6200012b90a8ep
-1, 0x1.904ab0644b605p
-55},
136 {0x1.66000045734a6p
-1, 0x1.1ff9bea62f7a9p
-57},
137 {0x1.69fffc325f2c5p
-1, 0x1.27ecfcb3c90bap
-55},
138 {0x1.6e00038b95a04p
-1, 0x1.8ff8856739326p
-55},
139 {0x1.71fffe09994e3p
-1, 0x1.afd40275f82b1p
-55},
140 {0x1.7600015590e1p
-1, -0x1.2fd75b4238341p
-56},
141 {0x1.7a00012655bd5p
-1, 0x1.808e67c242b76p
-56},
142 {0x1.7e0003259e9a6p
-1, -0x1.208e426f622b7p
-57},
143 {0x1.81fffedb4b2d2p
-1, -0x1.402461ea5c92fp
-55},
144 {0x1.860002dfafcc3p
-1, 0x1.df7f4a2f29a1fp
-57},
145 {0x1.89ffff78c6b5p
-1, -0x1.e0453094995fdp
-55},
146 {0x1.8e00039671566p
-1, -0x1.a04f3bec77b45p
-55},
147 {0x1.91fffe2bf1745p
-1, -0x1.7fa34400e203cp
-56},
148 {0x1.95fffcc5c9fd1p
-1, -0x1.6ff8005a0695dp
-56},
149 {0x1.9a0003bba4767p
-1, 0x1.0f8c4c4ec7e03p
-56},
150 {0x1.9dfffe7b92da5p
-1, 0x1.e7fd9478c4602p
-55},
151 {0x1.a1fffd72efdafp
-1, -0x1.a0c554dcdae7ep
-57},
152 {0x1.a5fffde04ff95p
-1, 0x1.67da98ce9b26bp
-55},
153 {0x1.a9fffca5e8d2bp
-1, -0x1.284c9b54c13dep
-55},
154 {0x1.adfffddad03eap
-1, 0x1.812c8ea602e3cp
-58},
155 {0x1.b1ffff10d3d4dp
-1, -0x1.efaddad27789cp
-55},
156 {0x1.b5fffce21165ap
-1, 0x1.3cb1719c61237p
-58},
157 {0x1.b9fffd950e674p
-1, 0x1.3f7d94194cep
-56},
158 {0x1.be000139ca8afp
-1, 0x1.50ac4215d9bcp
-56},
159 {0x1.c20005b46df99p
-1, 0x1.beea653e9c1c9p
-57},
160 {0x1.c600040b9f7aep
-1, -0x1.c079f274a70d6p
-56},
161 {0x1.ca0006255fd8ap
-1, -0x1.a0b4076e84c1fp
-56},
162 {0x1.cdfffd94c095dp
-1, 0x1.8f933f99ab5d7p
-55},
163 {0x1.d1ffff975d6cfp
-1, -0x1.82c08665fe1bep
-58},
164 {0x1.d5fffa2561c93p
-1, -0x1.b04289bd295f3p
-56},
165 {0x1.d9fff9d228b0cp
-1, 0x1.70251340fa236p
-55},
166 {0x1.de00065bc7e16p
-1, -0x1.5011e16a4d80cp
-56},
167 {0x1.e200002f64791p
-1, 0x1.9802f09ef62ep
-55},
168 {0x1.e600057d7a6d8p
-1, -0x1.e0b75580cf7fap
-56},
169 {0x1.ea00027edc00cp
-1, -0x1.c848309459811p
-55},
170 {0x1.ee0006cf5cb7cp
-1, -0x1.f8027951576f4p
-55},
171 {0x1.f2000782b7dccp
-1, -0x1.f81d97274538fp
-55},
172 {0x1.f6000260c450ap
-1, -0x1.071002727ffdcp
-59},
173 {0x1.f9fffe88cd533p
-1, -0x1.81bdce1fda8bp
-58},
174 {0x1.fdfffd50f8689p
-1, 0x1.7f91acb918e6ep
-55},
175 {0x1.0200004292367p
+0, 0x1.b7ff365324681p
-54},
176 {0x1.05fffe3e3d668p
+0, 0x1.6fa08ddae957bp
-55},
177 {0x1.0a0000a85a757p
+0, -0x1.7e2de80d3fb91p
-58},
178 {0x1.0e0001a5f3fccp
+0, -0x1.1823305c5f014p
-54},
179 {0x1.11ffff8afbaf5p
+0, -0x1.bfabb6680bac2p
-55},
180 {0x1.15fffe54d91adp
+0, -0x1.d7f121737e7efp
-54},
181 {0x1.1a00011ac36e1p
+0, 0x1.c000a0516f5ffp
-54},
182 {0x1.1e00019c84248p
+0, -0x1.082fbe4da5dap
-54},
183 {0x1.220000ffe5e6ep
+0, -0x1.8fdd04c9cfb43p
-55},
184 {0x1.26000269fd891p
+0, 0x1.cfe2a7994d182p
-55},
185 {0x1.2a00029a6e6dap
+0, -0x1.00273715e8bc5p
-56},
186 {0x1.2dfffe0293e39p
+0, 0x1.b7c39dab2a6f9p
-54},
187 {0x1.31ffff7dcf082p
+0, 0x1.df1336edc5254p
-56},
188 {0x1.35ffff05a8b6p
+0, -0x1.e03564ccd31ebp
-54},
189 {0x1.3a0002e0eaeccp
+0, 0x1.5f0e74bd3a477p
-56},
190 {0x1.3e000043bb236p
+0, 0x1.c7dcb149d8833p
-54},
191 {0x1.4200002d187ffp
+0, 0x1.e08afcf2d3d28p
-56},
192 {0x1.460000d387cb1p
+0, 0x1.20837856599a6p
-55},
193 {0x1.4a00004569f89p
+0, -0x1.9fa5c904fbcd2p
-55},
194 {0x1.4e000043543f3p
+0, -0x1.81125ed175329p
-56},
195 {0x1.51fffcc027f0fp
+0, 0x1.883d8847754dcp
-54},
196 {0x1.55ffffd87b36fp
+0, -0x1.709e731d02807p
-55},
197 {0x1.59ffff21df7bap
+0, 0x1.7f79f68727b02p
-55},
198 {0x1.5dfffebfc3481p
+0, -0x1.180902e30e93ep
-54},